A roller bearing comprises an outer ring, an inner ring, a plurality of rollers arranged between the outer ring and the inner ring, and a retainer retaining the plurality of rollers in general. The retainer retaining the rollers includes various kinds of retainers such as a resin retainer, a pressed retainer, a machined retainer, and a welded retainer based on a difference in material and production method, and they are used depending on their usage and characteristics. In addition, the retainer is an integrated type, that is, it comprises annular one component in general.
According to a roller bearing for supporting a main shaft of a wind-power generator provided with a blade for receiving the wind, since it needs to receive a high load, the roller bearing becomes also large. It means that each component member constituting the roller bearing such as a roller and a retainer becomes large, so that it becomes difficult to produce and assemble the member. In this case, when each member can be split, its production and assembling become easy.
Here, a technique regarding a split type retainer in which a retainer contained in the roller bearing is split along a split line extending in a direction along a shaft has been disclosed in European Patent Publication No. 1408248A2. FIG. 36 is a perspective view showing a retainer segment of the split type retainer disclosed in the European Patent Publication No. 1408248A2. Referring to FIG. 36, a retainer segment 101a has column parts 103a, 103b, 103c, 103d and 103e extending in a direction along a shaft so as to form a plurality of pockets 104 to hold rollers, and connection parts 102a and 102b extending in a circumferential direction so as to connect the plurality of column parts 103a to 103e. 
FIG. 37 is a sectional view showing a part of the roller bearing containing the retainer segment 101a shown in FIG. 36. Referring to FIGS. 36 and 37, a description will be made of the constitution of a roller bearing 111 containing the retainer segment 101a. The roller bearing 111 has an outer ring 112, an inner ring 113, a plurality of rollers 114, and the plurality of retainer segments 101a, 101b, 101c and the like. The plurality of rollers 114 are held by the plurality of retainer segments 101a and the like in the vicinity of a PCD (Pitch Circle Diameter) in which the rollers roll most stably. The retainer segment 101a holding the plurality of rollers 114 is arranged circumferentially so as to abut on the adjacent retainer segments 101b and 101c having the same configuration at its column parts 103a and 103e positioned on the circumferentially most outer side. The plurality of retainer segments 101a, 101b, 101c and the like are continuously lined with each other and incorporated in the roller bearing 111, whereby one annular retainer contained in the roller bearing 111 is formed.
The above one annular retainer is formed by lining the plurality of retainer segments continuously in the circumferential direction. When the one annular retainer is formed by lining the plurality of retainer segments in the circumferential direction, a circumferential gap in view of thermal expansion and the like is needed.
When the gap exists between the retainer segments after the roller bearing is assembled, the adjacent retainer segments collide against each other in the circumferential direction when the roller bearing is operated. In this case, the column part positioned at the end receives the circumferential load from the adjacent retainer segment and it is deformed.
This will be described with reference to FIGS. 36, 37 and 38. FIG. 38 is a view showing the vicinity of the column part 103a positioned at one end of the retainer segment 101a incorporated in the roller bearing, taken from the radial outer side, that is, from a direction shown by an arrow X in FIG. 37. In addition, the deformation of the column part 103a is shown with exaggeration in FIG. 38. Referring to FIGS. 36, 37 and 38, the retainer segment 101a receives the load from the circumferential direction, that is, from the direction shown by arrows Y in FIGS. 37 and 38 due to the collision against the adjacent retainer segment 101b. 
Here, the load from the retainer segment 101b is applied to the column part 103a positioned at the circumferential end in the retainer segment 101a. Since the column part 103a is not connected in the circumferential direction and vulnerable to the circumferential load, it is deformed to the side of the pocket 104. In this case, the circumferential inner side of the column part 103a, that is, an end face 109 of the pocket 104 enters the pocket 104. As a result, the roller could be locked and the retainer segment 101 could be damaged due to the abrasion of the column part 103a. 